Engineering: Tokyo’s Skycrapers Moved but didn’t Collapse

Engineering: Tokyo’s Skycrapers Moved but didn’t Collapse
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“Skyscrapers were ‘like trees blowing in the wind”


“…Building earthquake resistant structures is an ongoing challenge and Japan is continually designing for and sensitive to its earthquake prone location. Their research includes the E-Defense Shake Table in Japan which is one of the most prominent shaking tables associated with earthquake engineering research.

Structures such as the Yokohama Landmark Tower utilize earthquake resistant techniques incorporating a flexible structure to absorb the force of earthquakes. Also a simple roller bearing technique is often integrated into a design, isolating the base of a building and providing protection of various building and non-building structures against potentially damaging lateral impacts of strong earthquakes. Sometimes this metallic bearing support is adapted to provide seismic isolation for skyscrapers and buildings on soft ground.”


The principles of anti-seismic building

Buildings can be constructed upon a base of isolators, which are nothing more than a large set of shock absorbers often consisting of alternate layers of rubber and steel bonded together around a central core. These reduce the earthquake loads felt by the building and its occupants.

Tall structures, such as skyscrapers, are often less prone to damage than shorter ones, as they are naturally more flexible. When a quake strikes a tall building the energy will be dissipated by the flexing of the structure, which although disturbing for occupants will usually minimize the possibility of collapse.

Whatever the height of the building the energy mustn’t be allowed to concentrate in a particular area – each support element needs to be able to transfer and dissipate the energy, and with clever design the energy can be transferred back to the ground.

The strength of a structure will depend on the materials used and the design of the support structure. In line with the flexibility considerations it is best to use flexible materials as they can withstand more distortion without breaking. Steel and wood are better in this regard than concrete or masonry. Interconnecting support elements and support trusses, such as those used in the TransAmerica pyramid in San Francisco may be used to improve integrity.

Any solution is never 100% safe against earthquakes, but by testing models of designs on shake tables and monitoring the effects of minor quakes on existing buildings, design improvements can be made which will help improve safety. Of particular importance is the nature of the ground around the building, as this can modify the characteristics of the quake and create problems if the seismic frequency is close to the resonant frequency of the building. If measurements suggest that this could be a factor, then additional structural elements may be needed to alter the building’s characteristics.

Finally, designers should be ensure that services such as electricity, water and particularly gas are designed in such a way as to minimize the probability of causing fire or additional disruption. This may employ similar techniques to those used on buildings or incorporate cut off features.”


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